Generally speaking, biopsy needles fall into one of two types, an end cutting needle, commonly referred to as a "Menghini" needle, or, a side cut needle such as the type commercially known as "Tru-cut" needles. Fundamentally, an end cutting needle includes a hollow cutting cannula having an especially configured, circumferentially sharpened, open end at the distal portion thereof. A stylette is conventionally inserted into the hollow shaft of the cannula in its "at rest" or unactuated position and generally extends flush with the open cutting edge of the cannula to close the open end. With the stylette thus inserted, the end cutting needle is inserted into the patient until the needle reaches the site of the lesion where the biopsy specimen is to be taken. The stylette is withdrawn and the needle further inserted into the lesion with the result that tissue is cut and fills the now open cutting end of the cannula as it travels a slight distance through the lesion to collect the specimen. A suction device can be applied to the proximal portion of the cannula to withdraw the tissue sample thus taken. Alternatively, the cannula can be rotated to sever the tissue and the cannula withdrawn from the site. In a typical side cut needle, there is a "solid" inner cannula within an outer cannula and the inner cannula has a shaped pointed end with a cutting groove formed in the distal portion of the inner cannula behind the pointed end. The side cut needle is inserted into the patient until the needle reaches the site of the lesion where the biopsy sample is to be taken. The inner cannula is then advanced into the lesion to the point where the specimen is to be taken and rotated so that the cutting groove severs the tissue. The outer cannula advances over the inner cannula thus containing or entrapping the specimen within the groove of the inner cannula and the outer cannula, and the needle is then withdrawn from the site. There are many biopsy needle designs commercially available or described in the literature. For example, it is known to provide an inner cannula within the cutting cannula of the end cutting needle which uses movable jaws extending beyond the distal end of the cutting cannula to sever and extract the biopsy specimen. "Hybrid" cannulas are also known. Fundamentally, if the biopsy specimen is removed through the cutting end of the cannula it is known and will be referred to hereinafter as a "end-cutting" needle and if the sample is taken from the side of the needle, the needle will be referred to hereinafter as a "side-cutting" needle. The invention described herein is applicable to all end-cutting and side-cutting biopsy needles.
Because most biopsy needles reliably function to remove biopsy specimens, the major concern today with biopsy needles and the procedures governing the use thereof centers about hemorrhaging complications caused by or attributed to the biopsy. The complications arise from severing blood vessels while positioning the needle and while severing the specimens and the resultant bleeding caused thereby. To accurately guide the biopsy needle, percutaneous procedures have been developed to permit visual radiological observation of the instrument inside the body. In conjunction with CT guided biopsies, biopsy needles have been especially designed to provide good CT scanning images. An example of such a needle is disclosed in my earlier U.S. Pat. No. 4,708,147 dated Nov. 24, 1987 incorporated herein by reference. The reader may refer to may prior patent for a more detailed explanation of various hemorrhagic complications resulting from the organ from which the biopsy specimen is taken.
It is difficult to accurately estimate the incident rate of hemorrhagic complications with conventional biopsy needles because of the variations of the needle designs in use, the patient selection and the somewhat different biopsy techniques employed. However, support within the literature can be found for quoting a five percent (5%) complication rate in blind liver biopsies which may be perhaps even higher for blind kidney biopsies. In my studies of guided biopsies using image scanning techniques, I would estimate the complication rate to drop to about 1.5%. While this represents a significant decrease, this problem, to which my invention is directed, is not resolved.
Within the prior art, the use of gelatin as a substance for making medication capsules for internal use and adapted to be absorbed by enzyme action or other physiological processes within the body is well known. Also, the use of gelatin material for various surgical techniques has been well documented. In particular, the use of a gelatin material in a "sponge" form or as a foam is commercially available from the Upjohn Company under the trademark "Gelfoam". Gelfoam with and without thrombin, a protein which is active at the last stage of clot formation and functions to change fibrinogen to fibrin, has been used in surgery in virtually all organ systems including prostrate, brain, musculoskeletal, vascular graphs and other areas without adverse complications. The use of gelatin as a coating for a fabric, blood-vessel graft is disclosed in U.S. Pat. No. 3,106,483 to Kline et al dated Oct. 8, 1963, incorporated herein by reference.
The use of hardened gelatin as forming a part of a surgical instrument is disclosed in U.S. Pat. No. 3,358,684 to Marshall dated Dec. 19, 1967, incorporated by reference herein. In Marshall, the distal cutting edge of a cannula which is used as a parenteral injection device is formed from a thiolated gelatin material. Specifically, the gelatin distal tip punctures a vein, and eventually dissolves, leaving the proximal portion of the cannula within the vein for administrating parenteral solutions. The cannula can be thus left in situ without vein damage which would otherwise arise from the presence of a sharp needle or the removal of the needle. In this sense, the prior art recognizes that it is known to use gelatin as a surgical instrument which can be dissolved at the insertion site.